FIG. 6 shows an example of a production facility for producing sanitary ware by slip casting, in which slip prepared and purified in a raw material-preparation room 1 is fed to a casting room 2 by way of a slip supply main pipes 4 by slip feeding facilities 3. Each slip supply main pipe 4 branches off in the casting room 2 and is connected to a pouring pipe 6 of each casting machine 5. The ends of the slip supply main pipes 4 and pouring pipes 6 are of a blind construction.
FIG. 7 shows the composition of a slip pipe from the slip supply main pipe 4 to each of the pouring pipes 6 and the composition of a pipe arrangement within the casting machine 5, in which a plurality of molds 7 are mounted on the casting machine 5 and each mold 7 is connected to the pouring pipe 6 through a pouring hose 8 having a pouring valve 9. The slip which has been fed by the slip feeding facilities 3 is replenished in a head tank 11 within the casting machine 5 by way of a head tank replenishing valve 10, and is supplied from the head tank 11 to each mold 7 by way of a slip supply valve 12, a pouring pipe 6, a pouring valve 9 and a pouring hose 8. A slip tank 13 for recovering surplus slip produced in a slip discharge process is provided at the end of the pouring pipe 6 by way of a slip discharge pipe 14 in every casting machine 5.
In the above-described slip supply system, since one cycle of a slip casting using plaster molds requires a long time, say, one to three hours, a temperature of the slip within the slip supply main pipe 4 for use in the following cycle of casting drops and the basic properties of slip such as viscosity, a slip casting rate and the like change. If a casting operation is performed with the slip having changed in properties, there is a problem in that the thickness of the formed product changes and, when the formed product is removed from the plaster mold, it becomes deformed and is cracked. Such an inclination remarkably appears at the time of performing a casting operation after the stoppage of a long time, i.e., at the time of a commencement of work.
Further, there is a problem in that when slip remains for a long time at night or during a holiday, it adheres gradually to the inner wall of the pipe and forms solid matter. As such adhesion proceeds, an area of cross section of the pipe through which slip passes becomes small and brings about great resistance in the pipe. Thus, the time taken to supply slip to the plaster molds becomes longer and a casting cycle is extended.
Moreover, when a casting operation is performed, solid matter peels off from the inner wall of the pipe by a pressure of slip and is supplied to the interiors of the molds together with slip, thereby causing defects to be produced in the formed products. Particularly, the pouring pipe 6 of the casting machine 5 shown in FIG. 7 has a problem in that since the interior of the pipe becomes empty due to the discharge of slip, the slip adhered to the inner wall of the pipe is apt to dry and firmly stick thereto.
Further, when the casting machine 5 is allowed to stand in a condition of rest for a long time, there is a danger of the slip within the pipe becoming completely solidified to consequently clog the pipe, thereby making it impossible to use the pouring pipe 6 of the casting machine 5 and the slip supply main pipe 4 again.